In the anime, many children under the age of ten have been shown to own Pokémon, confusing viewers. It is generally an accepted fandom theory that minors under the age of ten may own Pokémon, but are not allowed to compete in Pokémon League-sanctioned tournaments or challenge Gym Leaders.

In the manga

In The Electric Tale of Pikachu

According to The Electric Tale of Pikachumanga, potential Trainers are required to attend a half-day training session before qualifying to take a brief test. Those who pass the examination receive the license. Only licensed Trainers are legally allowed to purchase Poké Balls.